1. Field of the Invention
This invention relates to a lift cylinder assembly and is particularly to an improved hydraulic cylinder arrangement that is particularly well suited for use with a marine outboard propulsion unit.
2. Description of the Related Art
Many types of marine propulsion units include a hydraulic motor assembly that is interposed between the outboard drive portion of the propulsion system and the watercraft transom. This hydraulic mechanism is provided for a number of purposes. The first of these purposes is to permit the outboard drive to pop-up when an underwater obstacle is struck so as to avoid damage to the lower unit. Once the underwater obstacle is cleared, the weight of the outboard drive returns it to its previous trim adjusted position.
In addition to this shock-absorbing function, the shock-absorbing mechanism is also constructed so as to preclude the outboard motor from popping-up when operated in reverse mode. That is, the pressure at which the shock absorber valve opens is chosen to be low enough to permit adequate shock-absorbing when underwater obstacles are struck, but high enough to resist the pop-up action when operating in reverse drive.
The functions can be achieved with relatively conventional shock absorbers. It is also desirable, however, to provide an arrangement wherein the marine propulsion unit can be hydraulically trimmed when operating under power. In addition, the hydraulic mechanism may also be employed for tilting the outboard drive up out of the water when not in use or for other purposes, such as for inspection.
Obviously, in order to permit trimming when operating under power, the hydraulic motor must provide large forces. This often is accomplished by providing relatively large effective piston areas over which the hydraulic pressure operates. Although providing good hydraulic force for trim operation, these types of mechanisms are very slow in tilt up operation.
Therefore, it has been proposed to employ one hydraulic motor that operates to provide the trim adjustment. This hydraulic motor has a relatively large diameter piston and, thus, has a relatively low stroke for a given fluid displacement. In addition, a smaller bore, but longer stroke, tilt fluid motor is also coupled to the outboard drive for effecting the tilt up operation. Thus, high speed tilting can be accomplished without loss of power for trim operation. These mechanisms are, however, quite complicated and require several fluid motors and control valve arrangements so as to actuate the proper motor when trim or tilt of the outboard motor is required.
Telescopic or compound hydraulic motors provide a single external cylinder to accomplish both the tilt and trim functions. A tilt cylinder is slidably supported in this outer or trim cylinder and it itself defines an internal cavity in which a tilt piston is provided. These systems basically operate by effecting hydraulic pressure actuation of both the trim and tilt cylinders simultaneously for a portion of the stroke during which the trim movement is accomplished. The tilt cylinder is then held and the tilt piston, which has a smaller effective piston area, is operated for tilt up operation.
One exemplary hydraulic cylinder arrangement will now be described for the reader's understanding of the conventional arrangement with particular reference to FIGS. 1A through 1E. This arrangement is also disclosed in the U.S. Pat. No. 5,718,613, which is hereby incorporated by reference.
FIGS. 1A through 1E illustrate in the five views the conditions at fully tilted and trimmed down position shown in FIG. 1A, through intermediate positions, to a fully trimmed up position shown in FIG. 1C, and to a fully tilted up position shown in FIG. 1E. This prior type of mechanism is indicated generally by the reference numeral 11 in these figures and is connected between a marine outboard drive, which may either constitute the outboard drive portion of an inboard-outboard drive or an outboard motor per se.
The combined tilt and trim fluid motor 11 includes an outer cylindrical housing assembly or tilt cylinder, indicated generally by the reference numeral 12 which has an integral trunion 13 having an opening 14 to pass a pivot pin for pivotal connection to the transom of the associated watercraft.
The tilt cylinder 12 defines an internal cavity 15 in which a tilt cylinder 16 is slidably supported. The tilt cylinder 16, in turn, divides the cylinder bore 15 of the cylinder housing 12 into an upper chamber 17 and a lower chamber 18. Suitable connections link the chambers 17, 18 with a hydraulic pressure circuit. Although a part of actual connections are formed at the wall portion of the outer cylinder 12 and not seen, inlet and outlet ports 19a, 19b are schematically indicated in these figures. The hydraulic pressure circuit is provided for pressurizing either the lower chamber 18 or the upper chamber 17 and depressurizing the other chamber in a known manner.
A tilt piston 20 is slidably supported within a bore 21 of the tilt cylinder 16. The tilt piston 20 has affixed to it a piston rod 22 that extends through openings in the end of the tilt cylinder 16 and the outer cylinder 23. A trunion 23 is provided on the exposed end of the piston rod 22. The trunion 23 has a bore 24 that is adapted to pass a pin (not shown) for providing a pivotal connection to the outboard drive.
Positioned in the tilt cylinder bore 21 below the piston 20 is a floating piston 25. The floating piston 25 is retained in the bore 21 below the tilt piston 20 by means that include a retainer device 26 which is urged by springs 26a toward the upper chamber 17. A latch operating mechanism 27 is interposed between the retainer device 26 and the floating piston 25 and cooperates with a plurality of detent balls 28. The detent balls 28 are adapted to engage corresponding recesses 29 in the outer cylinder 12 at the end of the trim stroke for locking the tilt cylinder 16 at this position, as FIG. 1D.
A shock absorber valve, indicated by the reference numeral 31, is carried by the tilt piston 20 and permits flow from the chamber formed above the tilt piston 20 within the tilt cylinder bore 21 to the area between the trim piston 19 and the floating piston 25. When an underwater obstacle is struck, the tilt piston 20 is urged upwardly and, if sufficient force is applied to open the shock absorber 31, fluid is displaced from the chamber in the trim piston cylinder bore 21 to the area between the tilt piston 29 and the floating piston 25. When this occurs, less fluid will be displaced from above the tilt piston 20 than below it and the floating piston 25 may move slightly upwardly.
Displacement of fluid from the chamber above the tilt piston 20 within the tilt cylinder bore 21 is precluded by a check valved passageway 32. This check valved passageway permits the piston 20 to act as a conventional shock absorber.
Once the underwater obstacle, which has been struck and has caused the popping up action has been cleared, the tilt piston 20 moves downwardly through the opening of a let down valve 33 which opens at a substantially lower pressure than the shock absorber valve 31. The let down valve 33 provides no significant damping and can be opened merely by the weight of the outboard drive acting on the tilt piston 20.
If the operator desires a trim up operation, the prior hydraulic mechanism shown in FIGS. 1A-1B is pressurized so that the chamber 18 below the floating piston 25 and tilt cylinder 16 will be pressurized. At the same time, the chamber 17 is depressurized by opening it to return. When the chamber 18 is pressurized, the fluid pressure acts upon the lower face of the tilt cylinder 16 and also on the floating piston 25 and on the tilt piston 20 to cause this assemblage to move upwardly as shown in FIG. 1B to a desired trim adjusted position. When the desired position is reached, then the pressurization is discontinued and the chambers 18, 17 are hydraulically locked so as to hold the new trim adjusted position. The shock-absorbing function previously described can operate with the drive positioned at a desired position in the trim range.
To effect trim down operation, the chamber 17 is pressurized and the chamber 18 is opened to return. The pressure of the driving force of the outboard drive can force the trim down operation without requiring hydraulic assist.
FIG. 1C shows the fully trimmed up position. In this position, the detent balls 28 are aligned with the recesses 29. At this same time, the tilt cylinder 16 will engage a stop at the upper end of the outer cylinder 12 so as to preclude further upward movement.
Tilt-up can be accomplished by continuing to pressurize the chamber 18 and opening the chamber 17 to return. However, since the check valve 32 would preclude the displacement of fluid from the tilt cylinder bore 21 by the tilt piston 20, a small valve actuating plunger 34 is provided within the tilt cylinder 16 to unseat the check valve 32 and permit upward movement of the tilt piston 20, as shown in FIG. 1D. When this continues, the retainer 29 will permit the detent balls 28 to be forced outwardly by a spring mechanism, which will be described later by reference to the actual detailed embodiment, and lock the tilt cylinder 16 in position. The reason for doing this will be described later.
Pressurization of the chamber 18 thus forces the floating piston 25 and tilt piston 20 to move upwardly. When this occurs, fluid is displaced past the open check valve 32 back to the return side.
The described construction provides a large effective area for trim operation and a smaller effective area for faster tilt-up operation. This tilt-up operation continues until the position shown in FIG. 1D. If tilt-down is then required, the chamber 18 is opened to return, and the chamber 17 may be pressurized. This pressure, however, will not cause the tilt cylinder 16 to move downwardly because the detent balls 28 in their receptive grooves 29 hold the tilt cylinder 16 against movement, and the mechanism will move back to the position shown in FIG. 1D. This permits faster tilt down than if the tilt cylinder 16 were also free to move downwardly.
This continues until the floating piston 25 and tilt piston 20 move to the position shown in FIG. 1C, wherein the detent balls 28 can again be released to permit trimming down to the desired position.
As has been noted above, when an underwater obstacle is struck the outboard drive, the popping up action is caused by this hydraulic mechanism and destruction of the outboard drive is prevented from occurring effectively. However, in the event that a massive obstacle is struck and huge force is abruptly exerted upon the outboard drive, tremendous pressure is produced in the tilt cylinder bore 21. If this pressure is beyond ability of the shock absorber valve 31, the piston rod 22 will be greatly restricted in its rapid upward motion. As a result, the outboard drive may not clear the obstacle smoothly. This gives rise to deterioration of durability of the outboard drive.
The aforenoted problem is not particular with the compound hydraulic mechanism and may occur, for example, with a single hydraulic mechanism that has only a tilt fluid motor.
For some occasion, foreign particles may enter the fluid and they can adversely affect the operation of the hydraulic device. For instance, under certain conditions, if a foreign particle is stuck at the shock absorber valve, fluid can pass through the valving passage without any intentional control and hence the hydraulic device may not hold the drive unit at an adjusted trim position. Also, the non-controlled fluid flow may damage the normal function of the hydraulic device.